docs: update README, API reference, dev-log, project structure with Agent monitoring + quick-alarm + latest fixes

- README.md: React 19, default pwd 123456, Docker Compose deploy, correct module list
- api-reference.md: add Agent monitoring section (report/latest/rules/quick-setup/alerts/tasks/kline)
- dev-log.md: new entry documenting hostname/IP fix, system collector, offline detection, quick alarm
- project-structure.md: add agent/ directory, dev-log.md link, React 19

frontend/src/App.tsx

@@ -31,6 +31,7 @@ import { AIPredictiveAnalytics } from '@/components/aiops/AIPredictiveAnalytics'
 import AlertCenter from '@/components/monitor/alert-center/AlertCenter';
 import TraceManager from '@/components/monitor/trace/TraceManager';
 import HostMonitorDashboard from '@/components/monitor/dashboard/HostMonitorDashboard';
+import GrafanaDashboard from '@/components/monitor/dashboard/GrafanaDashboard';
 import { MonitorCenter } from '@/pages/MonitorCenter';
 import { MetricsExplorer } from '@/pages/MetricsExplorer';
 import DatasourcePage from '@/components/monitor/datasource/DatasourcePage';
@@ -72,11 +73,11 @@ function App() {
             <Route path="deploy" element={<AppReleaseManager />} />
             {/* 监控告警 */}
             <Route path="metrics" element={<MetricsExplorer />} />
-            <Route path="alert-center" element={<AlertCenter />} />
-            <Route path="trace" element={<TraceManager />} />
-            <Route path="dashboards" element={<HostMonitorDashboard />} />
             <Route path="datasources" element={<DatasourcePage />} />
+            <Route path="trace" element={<TraceManager />} />
+            <Route path="dashboards" element={<GrafanaDashboard />} />
             <Route path="alerts" element={<AlertManager />} />
+            <Route path="alert-center" element={<AlertCenter />} />
             <Route path="logs" element={<AlertManager />} />
             <Route path="approval" element={<ApprovalFlowManager />} />
             {/* 自动化运维 */}